1. Field of the Invention
This invention is directed to pipe clamps; and in one aspect to a pipe clamp which is releasably lockable about a pipe.
2. Description of Related Art
The prior art discloses a variety of clamps for clamping pipe.
U.S. Pat. No. 4,743,056 discloses lifting tongs which are used in lifting heavy sections of cylindrical pipe. The lifting tongs have first and second opposing jaws and first and second mounting plates which are rigidly joined to the first and second jaws. The mounting plates are arranged in mutually overlapping parallel disposition in spaced separation from each other. First and second crank or cam levers are interposed in the gap between the mounting plates, and are rotatably secured relative thereto. The crank levers have cam lobes which act against corresponding cam surfaces on the jaws to force the jaws together with about a 4 to 1 mechanical advantage when the tongs are lifted.
U.S. Pat. No. 4,716,811 discloses a gripping apparatus for restraining the gun barrel on an armored vehicle which has a pair of gripping jaws pivotally supported within a housing and connected by a first pair of toggle links to a movable carriage within the housing such that the jaws are opened and closed upon movement of the carriage, a pair of locking members slidably carried on the carriage and adapted to enter apertures in the sides of the housing to lock the carriage at a predetermined location at which the jaws are closed and the toggle links of the first pair are in substantially a straight line relationship, and a second pair of toggle links connected to the locking member and to an actuator rod so as to enable the toggle links of the second pair to assume an over-center position upon the locking members being received in the apertures for positively locking the carriage in the predetermined location.
U.S. Pat. No. 4,545,722 discloses a flexible gripper for industrial robots through the use of articulated ball joint linkages and an industrial brake. The gripper can orient itself to an object and adapt to irregular surfaces while engaging the object. The gripper matches the orientation of the grasped part. With the object so engaged, the gripper is locked rigidly so that the orientation of the part is preserved as it is manipulated by the flexible gripper and its associated robot.
U.S. Pat. No. 4,647,098 discloses a hoist clamp with a coupling eye which has a gimbal-type connection by means of the shafts to clamp operating crank. When a diagonal pull is exerted, the neck of the coupling eye engages against a bracing point which is sufficiently high above the shaft to ensure that the lever action provides extra clamping force between the clamps. When the coupling eye swings about the shaft, the coupling eye engages against the upper edges of the casing, its edges curving outwards, so that additional clamping force is also obtained when the pull exerted is diagonal. Said additional clamping force is only marginally affected by the load held in the load aperture.
U.S. Pat. No. 3,451,711 discloses a set of pipe tongs for lifting and handling heavy sections of pipe, for example, installing the pipe in a narrow open trench or ditch. The tongs include means for automatically releasing the pipe after it is placed in the trench to facilitate withdrawal of the tongs. Upward force on arm members brings them into Contact with tong members, forcing the tong members toward each other to clamp a pipe therebetween.
There has long been a need for an effective pipe clamp which does not injure the pipe and from which pipe does not accidentally fall during lifting.